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Expression of matrix metalloproteinases (MMPs) by macrophages is a key determinant of plaque stability. Macrophages express soluble MMPs (e.g. MMP-9) and membrane-bound MT-MMPs. Whereas soluble MMPs are released as zymogens and are than activated by plasmin and other proteases, MT-MMPs are activated intracellular by furin-like convertases and then anchored to the cell surface as active enzymes. Activation of pro-MMP-2, which is not readily induced by cytokines that regulate other MMPs, depends on the formation of an MT-MMP/TIMP-2/MMP-2 complex on the cell surface. Macrophages express MT1-MMP and MMP-9, but little MMP-2, which is constitutively synthesized by VSMCs, potentially stored in the ECM. The aim of this study was to investigate the function of macrophages MT1-MMP for the activation of pro-MMP-2 potentially derived from other cells, as well as the role of the furin-like proprotein convertases (PCs; namely furin and PC5) in macrophages. Macrophage maturation of monocytic THP-1 cells (PMA 100 nM; 48h) was accompanied by increased MT1-MMP, as well as its activating enzymes furin and PC5. Inhibition of furin/PC5 with the pharmacological furin-like PC inhibitor dec-CMK inhibited MT1-MMP activation, but did not affect its sorting/routing to the cell surface. Monocytes synthesized little MMP-2 and MMP-9 and stimulation with TNF or LPS incresed only MMP-9. In contrast, macrophages abundantly expressed MMP-9 and some pro-MMP-2 activation was found in these MT1-MMP competent cells. However, this could not be further enhanced by stimulation with the TNF or LPS. Culturing of macrophages in medium derived from serum-straved VSMCs resulted in an enhanced pro-MMP-2 activation, whereas no activation was found when monocytes were used. This demonstrates, that pro-MMP-2 activation from VSMCs dependents on macrophage MT1-MMP. Activation of VSMC pro-MMP-2 by macrophage MT1-MMP was inhibited by a pharmacological furin-like PC inhibitor or a furin-silencing siRNA, as well as the MMP inhibitors GM6001 or an excess of TIMP-2. Immunohistochemistry demonstrated the colocalization of furin and PC5 with MT1-MMP in CD68 positive macrophages in human endarterectomy lesions and FACS analysis revealed the presence of furin, PC5 and MT1-MMP on PBMNCs obtained from healthy volunteers. Conclusion: The present study demonstrates, that furin/PC5 are central regulator of an MT1-MMP – pro-MMP-2 proteolytic amplification cascade, which requires interaction of macrophages and VSMCs.
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J. Vasc. Biol. 42, Sup:2 (2005) p21